A vacuum chuck as a holding apparatus to hold an object is conventionally used in general, but if the object is a thin plate, there is a problem that a periphery of the thin plate is deflected. In contrast, in an electrostatic holding apparatus such as an electrostatic chuck, because the object can be hold by an electrostatic force of the entirety of an electrode surface, even if the thin plate is handled to hold, a periphery of the thin plate is not deflected (for reference, see Patent Documents 1 and 2).
In the aforementioned electrostatic chuck, a holding part to hold the object is provided on a basic plate, and the holding part includes electrode element groups which provide a pair of positive and negative charges and an insulative layer fixed to the basic plate to cover the electrode element groups.
In such a structure, the object is held on a holding surface which is a surface of the insulative layer by an electrostatic attractive force induced between the object and the holding surface by applying a high voltage to the electrode element groups through a switch. When the switch is turned off, the electrostatic attractive force is removed to be disengaged the object from the holding surface. Thereby, the electrostatic chuck can attract an object such as a conductor, semi-conductor or high resistance by the electrostatic attractive force and allows the object to load or unload. Incidentally, an electrostatic chuck to hold an object in a floating state by controlling an attractive force by means of a control circuit or the like also is developed.
In such an electrostatic chuck, because a holding force for the object can be maintained even under a reduced pressure, the electrostatic chuck is applied to an alignment apparatus for substrate or joining apparatus for substrate or the like in a manufacturing process of a panel of a liquid display apparatus requiring an assembly under a reduced pressure (for reference, see Patent Documents 3 and 4).
For example, in an alignment apparatus described in patent document 3, an upper substrate W1 which is a workpiece of a mask or the like is configured to be held by an electrostatic attractive force of a substrate holder (electrostatic chuck), and a lower substrate W2 aligned together with the upper substrate W1 is configured to be supported on a lower stage approximately in a horizontal state.
The electrostatic chuck includes a flat plate-like basic member which is connected to an actuator such as a motor or the like and capable of moving in directions of x, y and z (vertical) axes and θ (rotational direction in an x-y plane). The basic member has a lower surface configured to fix a pair of positive and negative electrode element groups covered by an insulative material. A positive voltage and a negative voltage are applied to the electrode element groups and thereby the upper substrate W1 is electrostatically attracted to a holding surface which is a lower surface of the insulative material.
On the other hand, the electrostatic chuck/or stage is provided with a hole to monitor an aligned mark by a monitoring camera. Thereby, the lower substrate W2 is placed and fixedly supported on the stage, the upper substrate W1 is transported to the holding surface by means of a transporting device, and a plus V1 volt and a minus V1 volt are applied to the pair of electrode element groups. Thereby, the upper substrate W1 is electrostatically absorbed to the electrode element groups.
An alignment of the objects can be accomplished by lowering the electrostatic chuck in the direction of z axis by driving the actuator, approaching (or contacting) the upper substrate W1 and the lower substrate W2, measuring an amount of displacement based on information such as an alignment mark from the camera, driving the actuator depending on the measured amount of displacement and moving the upper substrate W1 and the lower substrate W2 so that the amount of displacement in the directions of x and y axes and θ is eliminated.    Patent Document 1: Japanese Patent Application Publication 2004-335811 (FIG. 11)    Patent Document 2: Japanese Patent Application Publication 2004-120921 (paragraph 0012)    Patent Document 3: Japanese Patent Application Publication 2004-176124 (FIGS. 3, 4)    Patent Document 4: Japanese Patent Application Publication 2002-357838